A suite of pelitic schists from the contact metamorphic aureole around the syenite stock at Ascutney Mountain, Vermont, shows a decrease in the amounts of cordierite, quartz, and andalusite and an increase in pleonaste and corundum as the contact is approached. Whole rock chemical analyses show a distinct SiO2 concentration gradient from the wall rocks toward the intrusion; however, the syenite has a higher weight percent SiO2 than the adjacent schists. It is suggested that silica diffused down an SiO2 activity gradient into the intrusive; other major oxide components were apparently immobile. The diffusion of silica was probably through intergranular fluids, and the amount of silica available for diffusion was governed by the solubilities of cordierite, andalusite, and quartz in the interstitial fluid.
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Nielson, D.L. Silica diffusion at Ascutney Mountain, Vermont. Contr. Mineral. and Petrol. 40, 141–148 (1973). https://doi.org/10.1007/BF00378171
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